1. Field of the Invention
This invention relates to optical switching, more particularly to electromechanical optical switching.
2. Background of the Invention
Optical switches are typically of two types: ON/OFF and routing. Routing switches such as those shown in U.S. Pat. Nos. 5,155,778 and 5,846,863, can connect an input to any one of several outputs. ON/OFF switches, such as those shown in U.S. Pat. Nos. 5,178,728 and 5,846,863, make or break the optical connection between a single input and a single output. Although routing switches are more optically efficient, because all available light is put to use, they are more difficult to manufacture and align optically than ON/OFF switches. One structure that is particularly adaptable to both uses is the digital micromirror device (DMD), because of its fast switching time and relative ease of manufacture.
ON/OFF switches fall into two further categories. Shutter switches block and unblock the optical path between the input and output. This blocking can be performed in many ways. The two most common are altering the transmission characteristics of the optical medium between input and output. Steering switches steer light from the input fiber into or out of the output fiber. These switches, like routing switches, are more difficult to manufacture: and align optically than shutter switches.
Typically, the shutter switches have far less loss than the steering switches. They normally operate with the DMD element, a highly reflective, individually addressable micromirror, being inserted or brought into proximity of the fibers to turn the switch OFF. When the switch must pass light, the metal element remains away from the fiber and the light travels with relatively low loss. Additionally, since the switch operates within the fiber, there is no alignment problems, which can also lead to loss.
The steering switches typically only pass light from fiber to fiber if the DMD is ON. In one arrangement, the optical system is configured with the input and output fibers mounted at an angle to each other. The DMD is arranged at the intersection of the optical paths of the sending and receiving fiber, and light is bounced off of an ON DMD and to the receiving fiber. Another arrangement consists of a DMD arranged "over" the two fibers, so the light must be reflected out of the plane of the fibers and bounced off of an ON DMD element back to the plane of the receiving fiber. This contributes to loss, both from misalignment, which becomes a far greater possibility in this architecture, and the reflection loss from the mirror. The angling of the fibers and the package has other disadvantages as well, especially the difficulty in manufacturing, due to alignment problems, and the resultant bulky package.
Therefore, a need exists for an ON/OFF shutter switch between fibers that has the same advantages as other shutter switches such as ease of collinear alignment, less loss, and manufacturability.